Light-assisted self-organization and pattern formation in thin films of azobenzene-containing polyurea

In this work, ordered patterns having nanoscale features and resolutions in the range of 5-75 mu m are produced from thin films of azo-polyurea (azo-PU) using photoinduced dewetting. Azo-PU is synthesized through polyaddition reactions, and reversible isomerization between cis - trans states is demonstrated by exposure to light of wavelengths 365 and 450 nm. This photochemical response is exploited to produce patterns by selective exposure using photomasks followed by subsequent annealing to induce polymer flow and dewetting. Marangoni flow is found to be a dominant mechanism that controls morphological evolution of patterns. The patterns can be switched between pillar-like and hole-like morphologies by stimulating the forward or backward isomerization reaction, and pattern resolution can be controlled using photomasks of different feature sizes. Preferential adsorption of proteins on these patterns is proposed as a potential application.